Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2647 insertions, 0 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
new file mode 100644
index 0000000000..434fab3067
--- /dev/null
+++ b/drivers/block/xen-blkfront.c
@@ -0,0 +1,2647 @@
+/*
+ * blkfront.c
+ *
+ * XenLinux virtual block device driver.
+ *
+ * Copyright (c) 2003-2004, Keir Fraser & Steve Hand
+ * Modifications by Mark A. Williamson are (c) Intel Research Cambridge
+ * Copyright (c) 2004, Christian Limpach
+ * Copyright (c) 2004, Andrew Warfield
+ * Copyright (c) 2005, Christopher Clark
+ * Copyright (c) 2005, XenSource Ltd
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/interrupt.h>
+#include <linux/blkdev.h>
+#include <linux/blk-mq.h>
+#include <linux/hdreg.h>
+#include <linux/cdrom.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/major.h>
+#include <linux/mutex.h>
+#include <linux/scatterlist.h>
+#include <linux/bitmap.h>
+#include <linux/list.h>
+#include <linux/workqueue.h>
+#include <linux/sched/mm.h>
+
+#include <xen/xen.h>
+#include <xen/xenbus.h>
+#include <xen/grant_table.h>
+#include <xen/events.h>
+#include <xen/page.h>
+#include <xen/platform_pci.h>
+
+#include <xen/interface/grant_table.h>
+#include <xen/interface/io/blkif.h>
+#include <xen/interface/io/protocols.h>
+
+#include <asm/xen/hypervisor.h>
+
+/*
+ * The minimal size of segment supported by the block framework is PAGE_SIZE.
+ * When Linux is using a different page size than Xen, it may not be possible
+ * to put all the data in a single segment.
+ * This can happen when the backend doesn't support indirect descriptor and
+ * therefore the maximum amount of data that a request can carry is
+ * BLKIF_MAX_SEGMENTS_PER_REQUEST * XEN_PAGE_SIZE = 44KB
+ *
+ * Note that we only support one extra request. So the Linux page size
+ * should be <= ( 2 * BLKIF_MAX_SEGMENTS_PER_REQUEST * XEN_PAGE_SIZE) =
+ * 88KB.
+ */
+#define HAS_EXTRA_REQ (BLKIF_MAX_SEGMENTS_PER_REQUEST < XEN_PFN_PER_PAGE)
+
+enum blkif_state {
+	BLKIF_STATE_DISCONNECTED,
+	BLKIF_STATE_CONNECTED,
+	BLKIF_STATE_SUSPENDED,
+	BLKIF_STATE_ERROR,
+};
+
+struct grant {
+	grant_ref_t gref;
+	struct page *page;
+	struct list_head node;
+};
+
+enum blk_req_status {
+	REQ_PROCESSING,
+	REQ_WAITING,
+	REQ_DONE,
+	REQ_ERROR,
+	REQ_EOPNOTSUPP,
+};
+
+struct blk_shadow {
+	struct blkif_request req;
+	struct request *request;
+	struct grant **grants_used;
+	struct grant **indirect_grants;
+	struct scatterlist *sg;
+	unsigned int num_sg;
+	enum blk_req_status status;
+
+	#define NO_ASSOCIATED_ID ~0UL
+	/*
+	 * Id of the sibling if we ever need 2 requests when handling a
+	 * block I/O request
+	 */
+	unsigned long associated_id;
+};
+
+struct blkif_req {
+	blk_status_t	error;
+};
+
+static inline struct blkif_req *blkif_req(struct request *rq)
+{
+	return blk_mq_rq_to_pdu(rq);
+}
+
+static DEFINE_MUTEX(blkfront_mutex);
+static const struct block_device_operations xlvbd_block_fops;
+static struct delayed_work blkfront_work;
+static LIST_HEAD(info_list);
+
+/*
+ * Maximum number of segments in indirect requests, the actual value used by
+ * the frontend driver is the minimum of this value and the value provided
+ * by the backend driver.
+ */
+
+static unsigned int xen_blkif_max_segments = 32;
+module_param_named(max_indirect_segments, xen_blkif_max_segments, uint, 0444);
+MODULE_PARM_DESC(max_indirect_segments,
+		 "Maximum amount of segments in indirect requests (default is 32)");
+
+static unsigned int xen_blkif_max_queues = 4;
+module_param_named(max_queues, xen_blkif_max_queues, uint, 0444);
+MODULE_PARM_DESC(max_queues, "Maximum number of hardware queues/rings used per virtual disk");
+
+/*
+ * Maximum order of pages to be used for the shared ring between front and
+ * backend, 4KB page granularity is used.
+ */
+static unsigned int xen_blkif_max_ring_order;
+module_param_named(max_ring_page_order, xen_blkif_max_ring_order, int, 0444);
+MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the shared ring");
+
+static bool __read_mostly xen_blkif_trusted = true;
+module_param_named(trusted, xen_blkif_trusted, bool, 0644);
+MODULE_PARM_DESC(trusted, "Is the backend trusted");
+
+#define BLK_RING_SIZE(info)	\
+	__CONST_RING_SIZE(blkif, XEN_PAGE_SIZE * (info)->nr_ring_pages)
+
+/*
+ * ring-ref%u i=(-1UL) would take 11 characters + 'ring-ref' is 8, so 19
+ * characters are enough. Define to 20 to keep consistent with backend.
+ */
+#define RINGREF_NAME_LEN (20)
+/*
+ * queue-%u would take 7 + 10(UINT_MAX) = 17 characters.
+ */
+#define QUEUE_NAME_LEN (17)
+
+/*
+ *  Per-ring info.
+ *  Every blkfront device can associate with one or more blkfront_ring_info,
+ *  depending on how many hardware queues/rings to be used.
+ */
+struct blkfront_ring_info {
+	/* Lock to protect data in every ring buffer. */
+	spinlock_t ring_lock;
+	struct blkif_front_ring ring;
+	unsigned int ring_ref[XENBUS_MAX_RING_GRANTS];
+	unsigned int evtchn, irq;
+	struct work_struct work;
+	struct gnttab_free_callback callback;
+	struct list_head indirect_pages;
+	struct list_head grants;
+	unsigned int persistent_gnts_c;
+	unsigned long shadow_free;
+	struct blkfront_info *dev_info;
+	struct blk_shadow shadow[];
+};
+
+/*
+ * We have one of these per vbd, whether ide, scsi or 'other'.  They
+ * hang in private_data off the gendisk structure. We may end up
+ * putting all kinds of interesting stuff here :-)
+ */
+struct blkfront_info
+{
+	struct mutex mutex;
+	struct xenbus_device *xbdev;
+	struct gendisk *gd;
+	u16 sector_size;
+	unsigned int physical_sector_size;
+	unsigned long vdisk_info;
+	int vdevice;
+	blkif_vdev_t handle;
+	enum blkif_state connected;
+	/* Number of pages per ring buffer. */
+	unsigned int nr_ring_pages;
+	struct request_queue *rq;
+	unsigned int feature_flush:1;
+	unsigned int feature_fua:1;
+	unsigned int feature_discard:1;
+	unsigned int feature_secdiscard:1;
+	/* Connect-time cached feature_persistent parameter */
+	unsigned int feature_persistent_parm:1;
+	/* Persistent grants feature negotiation result */
+	unsigned int feature_persistent:1;
+	unsigned int bounce:1;
+	unsigned int discard_granularity;
+	unsigned int discard_alignment;
+	/* Number of 4KB segments handled */
+	unsigned int max_indirect_segments;
+	int is_ready;
+	struct blk_mq_tag_set tag_set;
+	struct blkfront_ring_info *rinfo;
+	unsigned int nr_rings;
+	unsigned int rinfo_size;
+	/* Save uncomplete reqs and bios for migration. */
+	struct list_head requests;
+	struct bio_list bio_list;
+	struct list_head info_list;
+};
+
+static unsigned int nr_minors;
+static unsigned long *minors;
+static DEFINE_SPINLOCK(minor_lock);
+
+#define PARTS_PER_DISK		16
+#define PARTS_PER_EXT_DISK      256
+
+#define BLKIF_MAJOR(dev) ((dev)>>8)
+#define BLKIF_MINOR(dev) ((dev) & 0xff)
+
+#define EXT_SHIFT 28
+#define EXTENDED (1<<EXT_SHIFT)
+#define VDEV_IS_EXTENDED(dev) ((dev)&(EXTENDED))
+#define BLKIF_MINOR_EXT(dev) ((dev)&(~EXTENDED))
+#define EMULATED_HD_DISK_MINOR_OFFSET (0)
+#define EMULATED_HD_DISK_NAME_OFFSET (EMULATED_HD_DISK_MINOR_OFFSET / 256)
+#define EMULATED_SD_DISK_MINOR_OFFSET (0)
+#define EMULATED_SD_DISK_NAME_OFFSET (EMULATED_SD_DISK_MINOR_OFFSET / 256)
+
+#define DEV_NAME	"xvd"	/* name in /dev */
+
+/*
+ * Grants are always the same size as a Xen page (i.e 4KB).
+ * A physical segment is always the same size as a Linux page.
+ * Number of grants per physical segment
+ */
+#define GRANTS_PER_PSEG	(PAGE_SIZE / XEN_PAGE_SIZE)
+
+#define GRANTS_PER_INDIRECT_FRAME \
+	(XEN_PAGE_SIZE / sizeof(struct blkif_request_segment))
+
+#define INDIRECT_GREFS(_grants)		\
+	DIV_ROUND_UP(_grants, GRANTS_PER_INDIRECT_FRAME)
+
+static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo);
+static void blkfront_gather_backend_features(struct blkfront_info *info);
+static int negotiate_mq(struct blkfront_info *info);
+
+#define for_each_rinfo(info, ptr, idx)				\
+	for ((ptr) = (info)->rinfo, (idx) = 0;			\
+	     (idx) < (info)->nr_rings;				\
+	     (idx)++, (ptr) = (void *)(ptr) + (info)->rinfo_size)
+
+static inline struct blkfront_ring_info *
+get_rinfo(const struct blkfront_info *info, unsigned int i)
+{
+	BUG_ON(i >= info->nr_rings);
+	return (void *)info->rinfo + i * info->rinfo_size;
+}
+
+static int get_id_from_freelist(struct blkfront_ring_info *rinfo)
+{
+	unsigned long free = rinfo->shadow_free;
+
+	BUG_ON(free >= BLK_RING_SIZE(rinfo->dev_info));
+	rinfo->shadow_free = rinfo->shadow[free].req.u.rw.id;
+	rinfo->shadow[free].req.u.rw.id = 0x0fffffee; /* debug */
+	return free;
+}
+
+static int add_id_to_freelist(struct blkfront_ring_info *rinfo,
+			      unsigned long id)
+{
+	if (rinfo->shadow[id].req.u.rw.id != id)
+		return -EINVAL;
+	if (rinfo->shadow[id].request == NULL)
+		return -EINVAL;
+	rinfo->shadow[id].req.u.rw.id  = rinfo->shadow_free;
+	rinfo->shadow[id].request = NULL;
+	rinfo->shadow_free = id;
+	return 0;
+}
+
+static int fill_grant_buffer(struct blkfront_ring_info *rinfo, int num)
+{
+	struct blkfront_info *info = rinfo->dev_info;
+	struct page *granted_page;
+	struct grant *gnt_list_entry, *n;
+	int i = 0;
+
+	while (i < num) {
+		gnt_list_entry = kzalloc(sizeof(struct grant), GFP_NOIO);
+		if (!gnt_list_entry)
+			goto out_of_memory;
+
+		if (info->bounce) {
+			granted_page = alloc_page(GFP_NOIO | __GFP_ZERO);
+			if (!granted_page) {
+				kfree(gnt_list_entry);
+				goto out_of_memory;
+			}
+			gnt_list_entry->page = granted_page;
+		}
+
+		gnt_list_entry->gref = INVALID_GRANT_REF;
+		list_add(&gnt_list_entry->node, &rinfo->grants);
+		i++;
+	}
+
+	return 0;
+
+out_of_memory:
+	list_for_each_entry_safe(gnt_list_entry, n,
+	                         &rinfo->grants, node) {
+		list_del(&gnt_list_entry->node);
+		if (info->bounce)
+			__free_page(gnt_list_entry->page);
+		kfree(gnt_list_entry);
+		i--;
+	}
+	BUG_ON(i != 0);
+	return -ENOMEM;
+}
+
+static struct grant *get_free_grant(struct blkfront_ring_info *rinfo)
+{
+	struct grant *gnt_list_entry;
+
+	BUG_ON(list_empty(&rinfo->grants));
+	gnt_list_entry = list_first_entry(&rinfo->grants, struct grant,
+					  node);
+	list_del(&gnt_list_entry->node);
+
+	if (gnt_list_entry->gref != INVALID_GRANT_REF)
+		rinfo->persistent_gnts_c--;
+
+	return gnt_list_entry;
+}
+
+static inline void grant_foreign_access(const struct grant *gnt_list_entry,
+					const struct blkfront_info *info)
+{
+	gnttab_page_grant_foreign_access_ref_one(gnt_list_entry->gref,
+						 info->xbdev->otherend_id,
+						 gnt_list_entry->page,
+						 0);
+}
+
+static struct grant *get_grant(grant_ref_t *gref_head,
+			       unsigned long gfn,
+			       struct blkfront_ring_info *rinfo)
+{
+	struct grant *gnt_list_entry = get_free_grant(rinfo);
+	struct blkfront_info *info = rinfo->dev_info;
+
+	if (gnt_list_entry->gref != INVALID_GRANT_REF)
+		return gnt_list_entry;
+
+	/* Assign a gref to this page */
+	gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
+	BUG_ON(gnt_list_entry->gref == -ENOSPC);
+	if (info->bounce)
+		grant_foreign_access(gnt_list_entry, info);
+	else {
+		/* Grant access to the GFN passed by the caller */
+		gnttab_grant_foreign_access_ref(gnt_list_entry->gref,
+						info->xbdev->otherend_id,
+						gfn, 0);
+	}
+
+	return gnt_list_entry;
+}
+
+static struct grant *get_indirect_grant(grant_ref_t *gref_head,
+					struct blkfront_ring_info *rinfo)
+{
+	struct grant *gnt_list_entry = get_free_grant(rinfo);
+	struct blkfront_info *info = rinfo->dev_info;
+
+	if (gnt_list_entry->gref != INVALID_GRANT_REF)
+		return gnt_list_entry;
+
+	/* Assign a gref to this page */
+	gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
+	BUG_ON(gnt_list_entry->gref == -ENOSPC);
+	if (!info->bounce) {
+		struct page *indirect_page;
+
+		/* Fetch a pre-allocated page to use for indirect grefs */
+		BUG_ON(list_empty(&rinfo->indirect_pages));
+		indirect_page = list_first_entry(&rinfo->indirect_pages,
+						 struct page, lru);
+		list_del(&indirect_page->lru);
+		gnt_list_entry->page = indirect_page;
+	}
+	grant_foreign_access(gnt_list_entry, info);
+
+	return gnt_list_entry;
+}
+
+static const char *op_name(int op)
+{
+	static const char *const names[] = {
+		[BLKIF_OP_READ] = "read",
+		[BLKIF_OP_WRITE] = "write",
+		[BLKIF_OP_WRITE_BARRIER] = "barrier",
+		[BLKIF_OP_FLUSH_DISKCACHE] = "flush",
+		[BLKIF_OP_DISCARD] = "discard" };
+
+	if (op < 0 || op >= ARRAY_SIZE(names))
+		return "unknown";
+
+	if (!names[op])
+		return "reserved";
+
+	return names[op];
+}
+static int xlbd_reserve_minors(unsigned int minor, unsigned int nr)
+{
+	unsigned int end = minor + nr;
+	int rc;
+
+	if (end > nr_minors) {
+		unsigned long *bitmap, *old;
+
+		bitmap = kcalloc(BITS_TO_LONGS(end), sizeof(*bitmap),
+				 GFP_KERNEL);
+		if (bitmap == NULL)
+			return -ENOMEM;
+
+		spin_lock(&minor_lock);
+		if (end > nr_minors) {
+			old = minors;
+			memcpy(bitmap, minors,
+			       BITS_TO_LONGS(nr_minors) * sizeof(*bitmap));
+			minors = bitmap;
+			nr_minors = BITS_TO_LONGS(end) * BITS_PER_LONG;
+		} else
+			old = bitmap;
+		spin_unlock(&minor_lock);
+		kfree(old);
+	}
+
+	spin_lock(&minor_lock);
+	if (find_next_bit(minors, end, minor) >= end) {
+		bitmap_set(minors, minor, nr);
+		rc = 0;
+	} else
+		rc = -EBUSY;
+	spin_unlock(&minor_lock);
+
+	return rc;
+}
+
+static void xlbd_release_minors(unsigned int minor, unsigned int nr)
+{
+	unsigned int end = minor + nr;
+
+	BUG_ON(end > nr_minors);
+	spin_lock(&minor_lock);
+	bitmap_clear(minors,  minor, nr);
+	spin_unlock(&minor_lock);
+}
+
+static void blkif_restart_queue_callback(void *arg)
+{
+	struct blkfront_ring_info *rinfo = (struct blkfront_ring_info *)arg;
+	schedule_work(&rinfo->work);
+}
+
+static int blkif_getgeo(struct block_device *bd, struct hd_geometry *hg)
+{
+	/* We don't have real geometry info, but let's at least return
+	   values consistent with the size of the device */
+	sector_t nsect = get_capacity(bd->bd_disk);
+	sector_t cylinders = nsect;
+
+	hg->heads = 0xff;
+	hg->sectors = 0x3f;
+	sector_div(cylinders, hg->heads * hg->sectors);
+	hg->cylinders = cylinders;
+	if ((sector_t)(hg->cylinders + 1) * hg->heads * hg->sectors < nsect)
+		hg->cylinders = 0xffff;
+	return 0;
+}
+
+static int blkif_ioctl(struct block_device *bdev, blk_mode_t mode,
+		       unsigned command, unsigned long argument)
+{
+	struct blkfront_info *info = bdev->bd_disk->private_data;
+	int i;
+
+	switch (command) {
+	case CDROMMULTISESSION:
+		for (i = 0; i < sizeof(struct cdrom_multisession); i++)
+			if (put_user(0, (char __user *)(argument + i)))
+				return -EFAULT;
+		return 0;
+	case CDROM_GET_CAPABILITY:
+		if (!(info->vdisk_info & VDISK_CDROM))
+			return -EINVAL;
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+static unsigned long blkif_ring_get_request(struct blkfront_ring_info *rinfo,
+					    struct request *req,
+					    struct blkif_request **ring_req)
+{
+	unsigned long id;
+
+	*ring_req = RING_GET_REQUEST(&rinfo->ring, rinfo->ring.req_prod_pvt);
+	rinfo->ring.req_prod_pvt++;
+
+	id = get_id_from_freelist(rinfo);
+	rinfo->shadow[id].request = req;
+	rinfo->shadow[id].status = REQ_PROCESSING;
+	rinfo->shadow[id].associated_id = NO_ASSOCIATED_ID;
+
+	rinfo->shadow[id].req.u.rw.id = id;
+
+	return id;
+}
+
+static int blkif_queue_discard_req(struct request *req, struct blkfront_ring_info *rinfo)
+{
+	struct blkfront_info *info = rinfo->dev_info;
+	struct blkif_request *ring_req, *final_ring_req;
+	unsigned long id;
+
+	/* Fill out a communications ring structure. */
+	id = blkif_ring_get_request(rinfo, req, &final_ring_req);
+	ring_req = &rinfo->shadow[id].req;
+
+	ring_req->operation = BLKIF_OP_DISCARD;
+	ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
+	ring_req->u.discard.id = id;
+	ring_req->u.discard.sector_number = (blkif_sector_t)blk_rq_pos(req);
+	if (req_op(req) == REQ_OP_SECURE_ERASE && info->feature_secdiscard)
+		ring_req->u.discard.flag = BLKIF_DISCARD_SECURE;
+	else
+		ring_req->u.discard.flag = 0;
+
+	/* Copy the request to the ring page. */
+	*final_ring_req = *ring_req;
+	rinfo->shadow[id].status = REQ_WAITING;
+
+	return 0;
+}
+
+struct setup_rw_req {
+	unsigned int grant_idx;
+	struct blkif_request_segment *segments;
+	struct blkfront_ring_info *rinfo;
+	struct blkif_request *ring_req;
+	grant_ref_t gref_head;
+	unsigned int id;
+	/* Only used when persistent grant is used and it's a write request */
+	bool need_copy;
+	unsigned int bvec_off;
+	char *bvec_data;
+
+	bool require_extra_req;
+	struct blkif_request *extra_ring_req;
+};
+
+static void blkif_setup_rw_req_grant(unsigned long gfn, unsigned int offset,
+				     unsigned int len, void *data)
+{
+	struct setup_rw_req *setup = data;
+	int n, ref;
+	struct grant *gnt_list_entry;
+	unsigned int fsect, lsect;
+	/* Convenient aliases */
+	unsigned int grant_idx = setup->grant_idx;
+	struct blkif_request *ring_req = setup->ring_req;
+	struct blkfront_ring_info *rinfo = setup->rinfo;
+	/*
+	 * We always use the shadow of the first request to store the list
+	 * of grant associated to the block I/O request. This made the
+	 * completion more easy to handle even if the block I/O request is
+	 * split.
+	 */
+	struct blk_shadow *shadow = &rinfo->shadow[setup->id];
+
+	if (unlikely(setup->require_extra_req &&
+		     grant_idx >= BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
+		/*
+		 * We are using the second request, setup grant_idx
+		 * to be the index of the segment array.
+		 */
+		grant_idx -= BLKIF_MAX_SEGMENTS_PER_REQUEST;
+		ring_req = setup->extra_ring_req;
+	}
+
+	if ((ring_req->operation == BLKIF_OP_INDIRECT) &&
+	    (grant_idx % GRANTS_PER_INDIRECT_FRAME == 0)) {
+		if (setup->segments)
+			kunmap_atomic(setup->segments);
+
+		n = grant_idx / GRANTS_PER_INDIRECT_FRAME;
+		gnt_list_entry = get_indirect_grant(&setup->gref_head, rinfo);
+		shadow->indirect_grants[n] = gnt_list_entry;
+		setup->segments = kmap_atomic(gnt_list_entry->page);
+		ring_req->u.indirect.indirect_grefs[n] = gnt_list_entry->gref;
+	}
+
+	gnt_list_entry = get_grant(&setup->gref_head, gfn, rinfo);
+	ref = gnt_list_entry->gref;
+	/*
+	 * All the grants are stored in the shadow of the first
+	 * request. Therefore we have to use the global index.
+	 */
+	shadow->grants_used[setup->grant_idx] = gnt_list_entry;
+
+	if (setup->need_copy) {
+		void *shared_data;
+
+		shared_data = kmap_atomic(gnt_list_entry->page);
+		/*
+		 * this does not wipe data stored outside the
+		 * range sg->offset..sg->offset+sg->length.
+		 * Therefore, blkback *could* see data from
+		 * previous requests. This is OK as long as
+		 * persistent grants are shared with just one
+		 * domain. It may need refactoring if this
+		 * changes
+		 */
+		memcpy(shared_data + offset,
+		       setup->bvec_data + setup->bvec_off,
+		       len);
+
+		kunmap_atomic(shared_data);
+		setup->bvec_off += len;
+	}
+
+	fsect = offset >> 9;
+	lsect = fsect + (len >> 9) - 1;
+	if (ring_req->operation != BLKIF_OP_INDIRECT) {
+		ring_req->u.rw.seg[grant_idx] =
+			(struct blkif_request_segment) {
+				.gref       = ref,
+				.first_sect = fsect,
+				.last_sect  = lsect };
+	} else {
+		setup->segments[grant_idx % GRANTS_PER_INDIRECT_FRAME] =
+			(struct blkif_request_segment) {
+				.gref       = ref,
+				.first_sect = fsect,
+				.last_sect  = lsect };
+	}
+
+	(setup->grant_idx)++;
+}
+
+static void blkif_setup_extra_req(struct blkif_request *first,
+				  struct blkif_request *second)
+{
+	uint16_t nr_segments = first->u.rw.nr_segments;
+
+	/*
+	 * The second request is only present when the first request uses
+	 * all its segments. It's always the continuity of the first one.
+	 */
+	first->u.rw.nr_segments = BLKIF_MAX_SEGMENTS_PER_REQUEST;
+
+	second->u.rw.nr_segments = nr_segments - BLKIF_MAX_SEGMENTS_PER_REQUEST;
+	second->u.rw.sector_number = first->u.rw.sector_number +
+		(BLKIF_MAX_SEGMENTS_PER_REQUEST * XEN_PAGE_SIZE) / 512;
+
+	second->u.rw.handle = first->u.rw.handle;
+	second->operation = first->operation;
+}
+
+static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *rinfo)
+{
+	struct blkfront_info *info = rinfo->dev_info;
+	struct blkif_request *ring_req, *extra_ring_req = NULL;
+	struct blkif_request *final_ring_req, *final_extra_ring_req = NULL;
+	unsigned long id, extra_id = NO_ASSOCIATED_ID;
+	bool require_extra_req = false;
+	int i;
+	struct setup_rw_req setup = {
+		.grant_idx = 0,
+		.segments = NULL,
+		.rinfo = rinfo,
+		.need_copy = rq_data_dir(req) && info->bounce,
+	};
+
+	/*
+	 * Used to store if we are able to queue the request by just using
+	 * existing persistent grants, or if we have to get new grants,
+	 * as there are not sufficiently many free.
+	 */
+	bool new_persistent_gnts = false;
+	struct scatterlist *sg;
+	int num_sg, max_grefs, num_grant;
+
+	max_grefs = req->nr_phys_segments * GRANTS_PER_PSEG;
+	if (max_grefs > BLKIF_MAX_SEGMENTS_PER_REQUEST)
+		/*
+		 * If we are using indirect segments we need to account
+		 * for the indirect grefs used in the request.
+		 */
+		max_grefs += INDIRECT_GREFS(max_grefs);
+
+	/* Check if we have enough persistent grants to allocate a requests */
+	if (rinfo->persistent_gnts_c < max_grefs) {
+		new_persistent_gnts = true;
+
+		if (gnttab_alloc_grant_references(
+		    max_grefs - rinfo->persistent_gnts_c,
+		    &setup.gref_head) < 0) {
+			gnttab_request_free_callback(
+				&rinfo->callback,
+				blkif_restart_queue_callback,
+				rinfo,
+				max_grefs - rinfo->persistent_gnts_c);
+			return 1;
+		}
+	}
+
+	/* Fill out a communications ring structure. */
+	id = blkif_ring_get_request(rinfo, req, &final_ring_req);
+	ring_req = &rinfo->shadow[id].req;
+
+	num_sg = blk_rq_map_sg(req->q, req, rinfo->shadow[id].sg);
+	num_grant = 0;
+	/* Calculate the number of grant used */
+	for_each_sg(rinfo->shadow[id].sg, sg, num_sg, i)
+	       num_grant += gnttab_count_grant(sg->offset, sg->length);
+
+	require_extra_req = info->max_indirect_segments == 0 &&
+		num_grant > BLKIF_MAX_SEGMENTS_PER_REQUEST;
+	BUG_ON(!HAS_EXTRA_REQ && require_extra_req);
+
+	rinfo->shadow[id].num_sg = num_sg;
+	if (num_grant > BLKIF_MAX_SEGMENTS_PER_REQUEST &&
+	    likely(!require_extra_req)) {
+		/*
+		 * The indirect operation can only be a BLKIF_OP_READ or
+		 * BLKIF_OP_WRITE
+		 */
+		BUG_ON(req_op(req) == REQ_OP_FLUSH || req->cmd_flags & REQ_FUA);
+		ring_req->operation = BLKIF_OP_INDIRECT;
+		ring_req->u.indirect.indirect_op = rq_data_dir(req) ?
+			BLKIF_OP_WRITE : BLKIF_OP_READ;
+		ring_req->u.indirect.sector_number = (blkif_sector_t)blk_rq_pos(req);
+		ring_req->u.indirect.handle = info->handle;
+		ring_req->u.indirect.nr_segments = num_grant;
+	} else {
+		ring_req->u.rw.sector_number = (blkif_sector_t)blk_rq_pos(req);
+		ring_req->u.rw.handle = info->handle;
+		ring_req->operation = rq_data_dir(req) ?
+			BLKIF_OP_WRITE : BLKIF_OP_READ;
+		if (req_op(req) == REQ_OP_FLUSH ||
+		    (req_op(req) == REQ_OP_WRITE && (req->cmd_flags & REQ_FUA))) {
+			/*
+			 * Ideally we can do an unordered flush-to-disk.
+			 * In case the backend onlysupports barriers, use that.
+			 * A barrier request a superset of FUA, so we can
+			 * implement it the same way.  (It's also a FLUSH+FUA,
+			 * since it is guaranteed ordered WRT previous writes.)
+			 */
+			if (info->feature_flush && info->feature_fua)
+				ring_req->operation =
+					BLKIF_OP_WRITE_BARRIER;
+			else if (info->feature_flush)
+				ring_req->operation =
+					BLKIF_OP_FLUSH_DISKCACHE;
+			else
+				ring_req->operation = 0;
+		}
+		ring_req->u.rw.nr_segments = num_grant;
+		if (unlikely(require_extra_req)) {
+			extra_id = blkif_ring_get_request(rinfo, req,
+							  &final_extra_ring_req);
+			extra_ring_req = &rinfo->shadow[extra_id].req;
+
+			/*
+			 * Only the first request contains the scatter-gather
+			 * list.
+			 */
+			rinfo->shadow[extra_id].num_sg = 0;
+
+			blkif_setup_extra_req(ring_req, extra_ring_req);
+
+			/* Link the 2 requests together */
+			rinfo->shadow[extra_id].associated_id = id;
+			rinfo->shadow[id].associated_id = extra_id;
+		}
+	}
+
+	setup.ring_req = ring_req;
+	setup.id = id;
+
+	setup.require_extra_req = require_extra_req;
+	if (unlikely(require_extra_req))
+		setup.extra_ring_req = extra_ring_req;
+
+	for_each_sg(rinfo->shadow[id].sg, sg, num_sg, i) {
+		BUG_ON(sg->offset + sg->length > PAGE_SIZE);
+
+		if (setup.need_copy) {
+			setup.bvec_off = sg->offset;
+			setup.bvec_data = kmap_atomic(sg_page(sg));
+		}
+
+		gnttab_foreach_grant_in_range(sg_page(sg),
+					      sg->offset,
+					      sg->length,
+					      blkif_setup_rw_req_grant,
+					      &setup);
+
+		if (setup.need_copy)
+			kunmap_atomic(setup.bvec_data);
+	}
+	if (setup.segments)
+		kunmap_atomic(setup.segments);
+
+	/* Copy request(s) to the ring page. */
+	*final_ring_req = *ring_req;
+	rinfo->shadow[id].status = REQ_WAITING;
+	if (unlikely(require_extra_req)) {
+		*final_extra_ring_req = *extra_ring_req;
+		rinfo->shadow[extra_id].status = REQ_WAITING;
+	}
+
+	if (new_persistent_gnts)
+		gnttab_free_grant_references(setup.gref_head);
+
+	return 0;
+}
+
+/*
+ * Generate a Xen blkfront IO request from a blk layer request.  Reads
+ * and writes are handled as expected.
+ *
+ * @req: a request struct
+ */
+static int blkif_queue_request(struct request *req, struct blkfront_ring_info *rinfo)
+{
+	if (unlikely(rinfo->dev_info->connected != BLKIF_STATE_CONNECTED))
+		return 1;
+
+	if (unlikely(req_op(req) == REQ_OP_DISCARD ||
+		     req_op(req) == REQ_OP_SECURE_ERASE))
+		return blkif_queue_discard_req(req, rinfo);
+	else
+		return blkif_queue_rw_req(req, rinfo);
+}
+
+static inline void flush_requests(struct blkfront_ring_info *rinfo)
+{
+	int notify;
+
+	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&rinfo->ring, notify);
+
+	if (notify)
+		notify_remote_via_irq(rinfo->irq);
+}
+
+static inline bool blkif_request_flush_invalid(struct request *req,
+					       struct blkfront_info *info)
+{
+	return (blk_rq_is_passthrough(req) ||
+		((req_op(req) == REQ_OP_FLUSH) &&
+		 !info->feature_flush) ||
+		((req->cmd_flags & REQ_FUA) &&
+		 !info->feature_fua));
+}
+
+static blk_status_t blkif_queue_rq(struct blk_mq_hw_ctx *hctx,
+			  const struct blk_mq_queue_data *qd)
+{
+	unsigned long flags;
+	int qid = hctx->queue_num;
+	struct blkfront_info *info = hctx->queue->queuedata;
+	struct blkfront_ring_info *rinfo = NULL;
+
+	rinfo = get_rinfo(info, qid);
+	blk_mq_start_request(qd->rq);
+	spin_lock_irqsave(&rinfo->ring_lock, flags);
+	if (RING_FULL(&rinfo->ring))
+		goto out_busy;
+
+	if (blkif_request_flush_invalid(qd->rq, rinfo->dev_info))
+		goto out_err;
+
+	if (blkif_queue_request(qd->rq, rinfo))
+		goto out_busy;
+
+	flush_requests(rinfo);
+	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+	return BLK_STS_OK;
+
+out_err:
+	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+	return BLK_STS_IOERR;
+
+out_busy:
+	blk_mq_stop_hw_queue(hctx);
+	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+	return BLK_STS_DEV_RESOURCE;
+}
+
+static void blkif_complete_rq(struct request *rq)
+{
+	blk_mq_end_request(rq, blkif_req(rq)->error);
+}
+
+static const struct blk_mq_ops blkfront_mq_ops = {
+	.queue_rq = blkif_queue_rq,
+	.complete = blkif_complete_rq,
+};
+
+static void blkif_set_queue_limits(struct blkfront_info *info)
+{
+	struct request_queue *rq = info->rq;
+	struct gendisk *gd = info->gd;
+	unsigned int segments = info->max_indirect_segments ? :
+				BLKIF_MAX_SEGMENTS_PER_REQUEST;
+
+	blk_queue_flag_set(QUEUE_FLAG_VIRT, rq);
+
+	if (info->feature_discard) {
+		blk_queue_max_discard_sectors(rq, get_capacity(gd));
+		rq->limits.discard_granularity = info->discard_granularity ?:
+						 info->physical_sector_size;
+		rq->limits.discard_alignment = info->discard_alignment;
+		if (info->feature_secdiscard)
+			blk_queue_max_secure_erase_sectors(rq,
+							   get_capacity(gd));
+	}
+
+	/* Hard sector size and max sectors impersonate the equiv. hardware. */
+	blk_queue_logical_block_size(rq, info->sector_size);
+	blk_queue_physical_block_size(rq, info->physical_sector_size);
+	blk_queue_max_hw_sectors(rq, (segments * XEN_PAGE_SIZE) / 512);
+
+	/* Each segment in a request is up to an aligned page in size. */
+	blk_queue_segment_boundary(rq, PAGE_SIZE - 1);
+	blk_queue_max_segment_size(rq, PAGE_SIZE);
+
+	/* Ensure a merged request will fit in a single I/O ring slot. */
+	blk_queue_max_segments(rq, segments / GRANTS_PER_PSEG);
+
+	/* Make sure buffer addresses are sector-aligned. */
+	blk_queue_dma_alignment(rq, 511);
+}
+
+static const char *flush_info(struct blkfront_info *info)
+{
+	if (info->feature_flush && info->feature_fua)
+		return "barrier: enabled;";
+	else if (info->feature_flush)
+		return "flush diskcache: enabled;";
+	else
+		return "barrier or flush: disabled;";
+}
+
+static void xlvbd_flush(struct blkfront_info *info)
+{
+	blk_queue_write_cache(info->rq, info->feature_flush ? true : false,
+			      info->feature_fua ? true : false);
+	pr_info("blkfront: %s: %s %s %s %s %s %s %s\n",
+		info->gd->disk_name, flush_info(info),
+		"persistent grants:", info->feature_persistent ?
+		"enabled;" : "disabled;", "indirect descriptors:",
+		info->max_indirect_segments ? "enabled;" : "disabled;",
+		"bounce buffer:", info->bounce ? "enabled" : "disabled;");
+}
+
+static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
+{
+	int major;
+	major = BLKIF_MAJOR(vdevice);
+	*minor = BLKIF_MINOR(vdevice);
+	switch (major) {
+		case XEN_IDE0_MAJOR:
+			*offset = (*minor / 64) + EMULATED_HD_DISK_NAME_OFFSET;
+			*minor = ((*minor / 64) * PARTS_PER_DISK) +
+				EMULATED_HD_DISK_MINOR_OFFSET;
+			break;
+		case XEN_IDE1_MAJOR:
+			*offset = (*minor / 64) + 2 + EMULATED_HD_DISK_NAME_OFFSET;
+			*minor = (((*minor / 64) + 2) * PARTS_PER_DISK) +
+				EMULATED_HD_DISK_MINOR_OFFSET;
+			break;
+		case XEN_SCSI_DISK0_MAJOR:
+			*offset = (*minor / PARTS_PER_DISK) + EMULATED_SD_DISK_NAME_OFFSET;
+			*minor = *minor + EMULATED_SD_DISK_MINOR_OFFSET;
+			break;
+		case XEN_SCSI_DISK1_MAJOR:
+		case XEN_SCSI_DISK2_MAJOR:
+		case XEN_SCSI_DISK3_MAJOR:
+		case XEN_SCSI_DISK4_MAJOR:
+		case XEN_SCSI_DISK5_MAJOR:
+		case XEN_SCSI_DISK6_MAJOR:
+		case XEN_SCSI_DISK7_MAJOR:
+			*offset = (*minor / PARTS_PER_DISK) + 
+				((major - XEN_SCSI_DISK1_MAJOR + 1) * 16) +
+				EMULATED_SD_DISK_NAME_OFFSET;
+			*minor = *minor +
+				((major - XEN_SCSI_DISK1_MAJOR + 1) * 16 * PARTS_PER_DISK) +
+				EMULATED_SD_DISK_MINOR_OFFSET;
+			break;
+		case XEN_SCSI_DISK8_MAJOR:
+		case XEN_SCSI_DISK9_MAJOR:
+		case XEN_SCSI_DISK10_MAJOR:
+		case XEN_SCSI_DISK11_MAJOR:
+		case XEN_SCSI_DISK12_MAJOR:
+		case XEN_SCSI_DISK13_MAJOR:
+		case XEN_SCSI_DISK14_MAJOR:
+		case XEN_SCSI_DISK15_MAJOR:
+			*offset = (*minor / PARTS_PER_DISK) + 
+				((major - XEN_SCSI_DISK8_MAJOR + 8) * 16) +
+				EMULATED_SD_DISK_NAME_OFFSET;
+			*minor = *minor +
+				((major - XEN_SCSI_DISK8_MAJOR + 8) * 16 * PARTS_PER_DISK) +
+				EMULATED_SD_DISK_MINOR_OFFSET;
+			break;
+		case XENVBD_MAJOR:
+			*offset = *minor / PARTS_PER_DISK;
+			break;
+		default:
+			printk(KERN_WARNING "blkfront: your disk configuration is "
+					"incorrect, please use an xvd device instead\n");
+			return -ENODEV;
+	}
+	return 0;
+}
+
+static char *encode_disk_name(char *ptr, unsigned int n)
+{
+	if (n >= 26)
+		ptr = encode_disk_name(ptr, n / 26 - 1);
+	*ptr = 'a' + n % 26;
+	return ptr + 1;
+}
+
+static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
+		struct blkfront_info *info, u16 sector_size,
+		unsigned int physical_sector_size)
+{
+	struct gendisk *gd;
+	int nr_minors = 1;
+	int err;
+	unsigned int offset;
+	int minor;
+	int nr_parts;
+	char *ptr;
+
+	BUG_ON(info->gd != NULL);
+	BUG_ON(info->rq != NULL);
+
+	if ((info->vdevice>>EXT_SHIFT) > 1) {
+		/* this is above the extended range; something is wrong */
+		printk(KERN_WARNING "blkfront: vdevice 0x%x is above the extended range; ignoring\n", info->vdevice);
+		return -ENODEV;
+	}
+
+	if (!VDEV_IS_EXTENDED(info->vdevice)) {
+		err = xen_translate_vdev(info->vdevice, &minor, &offset);
+		if (err)
+			return err;
+		nr_parts = PARTS_PER_DISK;
+	} else {
+		minor = BLKIF_MINOR_EXT(info->vdevice);
+		nr_parts = PARTS_PER_EXT_DISK;
+		offset = minor / nr_parts;
+		if (xen_hvm_domain() && offset < EMULATED_HD_DISK_NAME_OFFSET + 4)
+			printk(KERN_WARNING "blkfront: vdevice 0x%x might conflict with "
+					"emulated IDE disks,\n\t choose an xvd device name"
+					"from xvde on\n", info->vdevice);
+	}
+	if (minor >> MINORBITS) {
+		pr_warn("blkfront: %#x's minor (%#x) out of range; ignoring\n",
+			info->vdevice, minor);
+		return -ENODEV;
+	}
+
+	if ((minor % nr_parts) == 0)
+		nr_minors = nr_parts;
+
+	err = xlbd_reserve_minors(minor, nr_minors);
+	if (err)
+		return err;
+
+	memset(&info->tag_set, 0, sizeof(info->tag_set));
+	info->tag_set.ops = &blkfront_mq_ops;
+	info->tag_set.nr_hw_queues = info->nr_rings;
+	if (HAS_EXTRA_REQ && info->max_indirect_segments == 0) {
+		/*
+		 * When indirect descriptior is not supported, the I/O request
+		 * will be split between multiple request in the ring.
+		 * To avoid problems when sending the request, divide by
+		 * 2 the depth of the queue.
+		 */
+		info->tag_set.queue_depth =  BLK_RING_SIZE(info) / 2;
+	} else
+		info->tag_set.queue_depth = BLK_RING_SIZE(info);
+	info->tag_set.numa_node = NUMA_NO_NODE;
+	info->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
+	info->tag_set.cmd_size = sizeof(struct blkif_req);
+	info->tag_set.driver_data = info;
+
+	err = blk_mq_alloc_tag_set(&info->tag_set);
+	if (err)
+		goto out_release_minors;
+
+	gd = blk_mq_alloc_disk(&info->tag_set, info);
+	if (IS_ERR(gd)) {
+		err = PTR_ERR(gd);
+		goto out_free_tag_set;
+	}
+
+	strcpy(gd->disk_name, DEV_NAME);
+	ptr = encode_disk_name(gd->disk_name + sizeof(DEV_NAME) - 1, offset);
+	BUG_ON(ptr >= gd->disk_name + DISK_NAME_LEN);
+	if (nr_minors > 1)
+		*ptr = 0;
+	else
+		snprintf(ptr, gd->disk_name + DISK_NAME_LEN - ptr,
+			 "%d", minor & (nr_parts - 1));
+
+	gd->major = XENVBD_MAJOR;
+	gd->first_minor = minor;
+	gd->minors = nr_minors;
+	gd->fops = &xlvbd_block_fops;
+	gd->private_data = info;
+	set_capacity(gd, capacity);
+
+	info->rq = gd->queue;
+	info->gd = gd;
+	info->sector_size = sector_size;
+	info->physical_sector_size = physical_sector_size;
+	blkif_set_queue_limits(info);
+
+	xlvbd_flush(info);
+
+	if (info->vdisk_info & VDISK_READONLY)
+		set_disk_ro(gd, 1);
+	if (info->vdisk_info & VDISK_REMOVABLE)
+		gd->flags |= GENHD_FL_REMOVABLE;
+
+	return 0;
+
+out_free_tag_set:
+	blk_mq_free_tag_set(&info->tag_set);
+out_release_minors:
+	xlbd_release_minors(minor, nr_minors);
+	return err;
+}
+
+/* Already hold rinfo->ring_lock. */
+static inline void kick_pending_request_queues_locked(struct blkfront_ring_info *rinfo)
+{
+	if (!RING_FULL(&rinfo->ring))
+		blk_mq_start_stopped_hw_queues(rinfo->dev_info->rq, true);
+}
+
+static void kick_pending_request_queues(struct blkfront_ring_info *rinfo)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&rinfo->ring_lock, flags);
+	kick_pending_request_queues_locked(rinfo);
+	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+}
+
+static void blkif_restart_queue(struct work_struct *work)
+{
+	struct blkfront_ring_info *rinfo = container_of(work, struct blkfront_ring_info, work);
+
+	if (rinfo->dev_info->connected == BLKIF_STATE_CONNECTED)
+		kick_pending_request_queues(rinfo);
+}
+
+static void blkif_free_ring(struct blkfront_ring_info *rinfo)
+{
+	struct grant *persistent_gnt, *n;
+	struct blkfront_info *info = rinfo->dev_info;
+	int i, j, segs;
+
+	/*
+	 * Remove indirect pages, this only happens when using indirect
+	 * descriptors but not persistent grants
+	 */
+	if (!list_empty(&rinfo->indirect_pages)) {
+		struct page *indirect_page, *n;
+
+		BUG_ON(info->bounce);
+		list_for_each_entry_safe(indirect_page, n, &rinfo->indirect_pages, lru) {
+			list_del(&indirect_page->lru);
+			__free_page(indirect_page);
+		}
+	}
+
+	/* Remove all persistent grants. */
+	if (!list_empty(&rinfo->grants)) {
+		list_for_each_entry_safe(persistent_gnt, n,
+					 &rinfo->grants, node) {
+			list_del(&persistent_gnt->node);
+			if (persistent_gnt->gref != INVALID_GRANT_REF) {
+				gnttab_end_foreign_access(persistent_gnt->gref,
+							  NULL);
+				rinfo->persistent_gnts_c--;
+			}
+			if (info->bounce)
+				__free_page(persistent_gnt->page);
+			kfree(persistent_gnt);
+		}
+	}
+	BUG_ON(rinfo->persistent_gnts_c != 0);
+
+	for (i = 0; i < BLK_RING_SIZE(info); i++) {
+		/*
+		 * Clear persistent grants present in requests already
+		 * on the shared ring
+		 */
+		if (!rinfo->shadow[i].request)
+			goto free_shadow;
+
+		segs = rinfo->shadow[i].req.operation == BLKIF_OP_INDIRECT ?
+		       rinfo->shadow[i].req.u.indirect.nr_segments :
+		       rinfo->shadow[i].req.u.rw.nr_segments;
+		for (j = 0; j < segs; j++) {
+			persistent_gnt = rinfo->shadow[i].grants_used[j];
+			gnttab_end_foreign_access(persistent_gnt->gref, NULL);
+			if (info->bounce)
+				__free_page(persistent_gnt->page);
+			kfree(persistent_gnt);
+		}
+
+		if (rinfo->shadow[i].req.operation != BLKIF_OP_INDIRECT)
+			/*
+			 * If this is not an indirect operation don't try to
+			 * free indirect segments
+			 */
+			goto free_shadow;
+
+		for (j = 0; j < INDIRECT_GREFS(segs); j++) {
+			persistent_gnt = rinfo->shadow[i].indirect_grants[j];
+			gnttab_end_foreign_access(persistent_gnt->gref, NULL);
+			__free_page(persistent_gnt->page);
+			kfree(persistent_gnt);
+		}
+
+free_shadow:
+		kvfree(rinfo->shadow[i].grants_used);
+		rinfo->shadow[i].grants_used = NULL;
+		kvfree(rinfo->shadow[i].indirect_grants);
+		rinfo->shadow[i].indirect_grants = NULL;
+		kvfree(rinfo->shadow[i].sg);
+		rinfo->shadow[i].sg = NULL;
+	}
+
+	/* No more gnttab callback work. */
+	gnttab_cancel_free_callback(&rinfo->callback);
+
+	/* Flush gnttab callback work. Must be done with no locks held. */
+	flush_work(&rinfo->work);
+
+	/* Free resources associated with old device channel. */
+	xenbus_teardown_ring((void **)&rinfo->ring.sring, info->nr_ring_pages,
+			     rinfo->ring_ref);
+
+	if (rinfo->irq)
+		unbind_from_irqhandler(rinfo->irq, rinfo);
+	rinfo->evtchn = rinfo->irq = 0;
+}
+
+static void blkif_free(struct blkfront_info *info, int suspend)
+{
+	unsigned int i;
+	struct blkfront_ring_info *rinfo;
+
+	/* Prevent new requests being issued until we fix things up. */
+	info->connected = suspend ?
+		BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
+	/* No more blkif_request(). */
+	if (info->rq)
+		blk_mq_stop_hw_queues(info->rq);
+
+	for_each_rinfo(info, rinfo, i)
+		blkif_free_ring(rinfo);
+
+	kvfree(info->rinfo);
+	info->rinfo = NULL;
+	info->nr_rings = 0;
+}
+
+struct copy_from_grant {
+	const struct blk_shadow *s;
+	unsigned int grant_idx;
+	unsigned int bvec_offset;
+	char *bvec_data;
+};
+
+static void blkif_copy_from_grant(unsigned long gfn, unsigned int offset,
+				  unsigned int len, void *data)
+{
+	struct copy_from_grant *info = data;
+	char *shared_data;
+	/* Convenient aliases */
+	const struct blk_shadow *s = info->s;
+
+	shared_data = kmap_atomic(s->grants_used[info->grant_idx]->page);
+
+	memcpy(info->bvec_data + info->bvec_offset,
+	       shared_data + offset, len);
+
+	info->bvec_offset += len;
+	info->grant_idx++;
+
+	kunmap_atomic(shared_data);
+}
+
+static enum blk_req_status blkif_rsp_to_req_status(int rsp)
+{
+	switch (rsp)
+	{
+	case BLKIF_RSP_OKAY:
+		return REQ_DONE;
+	case BLKIF_RSP_EOPNOTSUPP:
+		return REQ_EOPNOTSUPP;
+	case BLKIF_RSP_ERROR:
+	default:
+		return REQ_ERROR;
+	}
+}
+
+/*
+ * Get the final status of the block request based on two ring response
+ */
+static int blkif_get_final_status(enum blk_req_status s1,
+				  enum blk_req_status s2)
+{
+	BUG_ON(s1 < REQ_DONE);
+	BUG_ON(s2 < REQ_DONE);
+
+	if (s1 == REQ_ERROR || s2 == REQ_ERROR)
+		return BLKIF_RSP_ERROR;
+	else if (s1 == REQ_EOPNOTSUPP || s2 == REQ_EOPNOTSUPP)
+		return BLKIF_RSP_EOPNOTSUPP;
+	return BLKIF_RSP_OKAY;
+}
+
+/*
+ * Return values:
+ *  1 response processed.
+ *  0 missing further responses.
+ * -1 error while processing.
+ */
+static int blkif_completion(unsigned long *id,
+			    struct blkfront_ring_info *rinfo,
+			    struct blkif_response *bret)
+{
+	int i = 0;
+	struct scatterlist *sg;
+	int num_sg, num_grant;
+	struct blkfront_info *info = rinfo->dev_info;
+	struct blk_shadow *s = &rinfo->shadow[*id];
+	struct copy_from_grant data = {
+		.grant_idx = 0,
+	};
+
+	num_grant = s->req.operation == BLKIF_OP_INDIRECT ?
+		s->req.u.indirect.nr_segments : s->req.u.rw.nr_segments;
+
+	/* The I/O request may be split in two. */
+	if (unlikely(s->associated_id != NO_ASSOCIATED_ID)) {
+		struct blk_shadow *s2 = &rinfo->shadow[s->associated_id];
+
+		/* Keep the status of the current response in shadow. */
+		s->status = blkif_rsp_to_req_status(bret->status);
+
+		/* Wait the second response if not yet here. */
+		if (s2->status < REQ_DONE)
+			return 0;
+
+		bret->status = blkif_get_final_status(s->status,
+						      s2->status);
+
+		/*
+		 * All the grants is stored in the first shadow in order
+		 * to make the completion code simpler.
+		 */
+		num_grant += s2->req.u.rw.nr_segments;
+
+		/*
+		 * The two responses may not come in order. Only the
+		 * first request will store the scatter-gather list.
+		 */
+		if (s2->num_sg != 0) {
+			/* Update "id" with the ID of the first response. */
+			*id = s->associated_id;
+			s = s2;
+		}
+
+		/*
+		 * We don't need anymore the second request, so recycling
+		 * it now.
+		 */
+		if (add_id_to_freelist(rinfo, s->associated_id))
+			WARN(1, "%s: can't recycle the second part (id = %ld) of the request\n",
+			     info->gd->disk_name, s->associated_id);
+	}
+
+	data.s = s;
+	num_sg = s->num_sg;
+
+	if (bret->operation == BLKIF_OP_READ && info->bounce) {
+		for_each_sg(s->sg, sg, num_sg, i) {
+			BUG_ON(sg->offset + sg->length > PAGE_SIZE);
+
+			data.bvec_offset = sg->offset;
+			data.bvec_data = kmap_atomic(sg_page(sg));
+
+			gnttab_foreach_grant_in_range(sg_page(sg),
+						      sg->offset,
+						      sg->length,
+						      blkif_copy_from_grant,
+						      &data);
+
+			kunmap_atomic(data.bvec_data);
+		}
+	}
+	/* Add the persistent grant into the list of free grants */
+	for (i = 0; i < num_grant; i++) {
+		if (!gnttab_try_end_foreign_access(s->grants_used[i]->gref)) {
+			/*
+			 * If the grant is still mapped by the backend (the
+			 * backend has chosen to make this grant persistent)
+			 * we add it at the head of the list, so it will be
+			 * reused first.
+			 */
+			if (!info->feature_persistent) {
+				pr_alert("backed has not unmapped grant: %u\n",
+					 s->grants_used[i]->gref);
+				return -1;
+			}
+			list_add(&s->grants_used[i]->node, &rinfo->grants);
+			rinfo->persistent_gnts_c++;
+		} else {
+			/*
+			 * If the grant is not mapped by the backend we add it
+			 * to the tail of the list, so it will not be picked
+			 * again unless we run out of persistent grants.
+			 */
+			s->grants_used[i]->gref = INVALID_GRANT_REF;
+			list_add_tail(&s->grants_used[i]->node, &rinfo->grants);
+		}
+	}
+	if (s->req.operation == BLKIF_OP_INDIRECT) {
+		for (i = 0; i < INDIRECT_GREFS(num_grant); i++) {
+			if (!gnttab_try_end_foreign_access(s->indirect_grants[i]->gref)) {
+				if (!info->feature_persistent) {
+					pr_alert("backed has not unmapped grant: %u\n",
+						 s->indirect_grants[i]->gref);
+					return -1;
+				}
+				list_add(&s->indirect_grants[i]->node, &rinfo->grants);
+				rinfo->persistent_gnts_c++;
+			} else {
+				struct page *indirect_page;
+
+				/*
+				 * Add the used indirect page back to the list of
+				 * available pages for indirect grefs.
+				 */
+				if (!info->bounce) {
+					indirect_page = s->indirect_grants[i]->page;
+					list_add(&indirect_page->lru, &rinfo->indirect_pages);
+				}
+				s->indirect_grants[i]->gref = INVALID_GRANT_REF;
+				list_add_tail(&s->indirect_grants[i]->node, &rinfo->grants);
+			}
+		}
+	}
+
+	return 1;
+}
+
+static irqreturn_t blkif_interrupt(int irq, void *dev_id)
+{
+	struct request *req;
+	struct blkif_response bret;
+	RING_IDX i, rp;
+	unsigned long flags;
+	struct blkfront_ring_info *rinfo = (struct blkfront_ring_info *)dev_id;
+	struct blkfront_info *info = rinfo->dev_info;
+	unsigned int eoiflag = XEN_EOI_FLAG_SPURIOUS;
+
+	if (unlikely(info->connected != BLKIF_STATE_CONNECTED)) {
+		xen_irq_lateeoi(irq, XEN_EOI_FLAG_SPURIOUS);
+		return IRQ_HANDLED;
+	}
+
+	spin_lock_irqsave(&rinfo->ring_lock, flags);
+ again:
+	rp = READ_ONCE(rinfo->ring.sring->rsp_prod);
+	virt_rmb(); /* Ensure we see queued responses up to 'rp'. */
+	if (RING_RESPONSE_PROD_OVERFLOW(&rinfo->ring, rp)) {
+		pr_alert("%s: illegal number of responses %u\n",
+			 info->gd->disk_name, rp - rinfo->ring.rsp_cons);
+		goto err;
+	}
+
+	for (i = rinfo->ring.rsp_cons; i != rp; i++) {
+		unsigned long id;
+		unsigned int op;
+
+		eoiflag = 0;
+
+		RING_COPY_RESPONSE(&rinfo->ring, i, &bret);
+		id = bret.id;
+
+		/*
+		 * The backend has messed up and given us an id that we would
+		 * never have given to it (we stamp it up to BLK_RING_SIZE -
+		 * look in get_id_from_freelist.
+		 */
+		if (id >= BLK_RING_SIZE(info)) {
+			pr_alert("%s: response has incorrect id (%ld)\n",
+				 info->gd->disk_name, id);
+			goto err;
+		}
+		if (rinfo->shadow[id].status != REQ_WAITING) {
+			pr_alert("%s: response references no pending request\n",
+				 info->gd->disk_name);
+			goto err;
+		}
+
+		rinfo->shadow[id].status = REQ_PROCESSING;
+		req  = rinfo->shadow[id].request;
+
+		op = rinfo->shadow[id].req.operation;
+		if (op == BLKIF_OP_INDIRECT)
+			op = rinfo->shadow[id].req.u.indirect.indirect_op;
+		if (bret.operation != op) {
+			pr_alert("%s: response has wrong operation (%u instead of %u)\n",
+				 info->gd->disk_name, bret.operation, op);
+			goto err;
+		}
+
+		if (bret.operation != BLKIF_OP_DISCARD) {
+			int ret;
+
+			/*
+			 * We may need to wait for an extra response if the
+			 * I/O request is split in 2
+			 */
+			ret = blkif_completion(&id, rinfo, &bret);
+			if (!ret)
+				continue;
+			if (unlikely(ret < 0))
+				goto err;
+		}
+
+		if (add_id_to_freelist(rinfo, id)) {
+			WARN(1, "%s: response to %s (id %ld) couldn't be recycled!\n",
+			     info->gd->disk_name, op_name(bret.operation), id);
+			continue;
+		}
+
+		if (bret.status == BLKIF_RSP_OKAY)
+			blkif_req(req)->error = BLK_STS_OK;
+		else
+			blkif_req(req)->error = BLK_STS_IOERR;
+
+		switch (bret.operation) {
+		case BLKIF_OP_DISCARD:
+			if (unlikely(bret.status == BLKIF_RSP_EOPNOTSUPP)) {
+				struct request_queue *rq = info->rq;
+
+				pr_warn_ratelimited("blkfront: %s: %s op failed\n",
+					   info->gd->disk_name, op_name(bret.operation));
+				blkif_req(req)->error = BLK_STS_NOTSUPP;
+				info->feature_discard = 0;
+				info->feature_secdiscard = 0;
+				blk_queue_max_discard_sectors(rq, 0);
+				blk_queue_max_secure_erase_sectors(rq, 0);
+			}
+			break;
+		case BLKIF_OP_FLUSH_DISKCACHE:
+		case BLKIF_OP_WRITE_BARRIER:
+			if (unlikely(bret.status == BLKIF_RSP_EOPNOTSUPP)) {
+				pr_warn_ratelimited("blkfront: %s: %s op failed\n",
+				       info->gd->disk_name, op_name(bret.operation));
+				blkif_req(req)->error = BLK_STS_NOTSUPP;
+			}
+			if (unlikely(bret.status == BLKIF_RSP_ERROR &&
+				     rinfo->shadow[id].req.u.rw.nr_segments == 0)) {
+				pr_warn_ratelimited("blkfront: %s: empty %s op failed\n",
+				       info->gd->disk_name, op_name(bret.operation));
+				blkif_req(req)->error = BLK_STS_NOTSUPP;
+			}
+			if (unlikely(blkif_req(req)->error)) {
+				if (blkif_req(req)->error == BLK_STS_NOTSUPP)
+					blkif_req(req)->error = BLK_STS_OK;
+				info->feature_fua = 0;
+				info->feature_flush = 0;
+				xlvbd_flush(info);
+			}
+			fallthrough;
+		case BLKIF_OP_READ:
+		case BLKIF_OP_WRITE:
+			if (unlikely(bret.status != BLKIF_RSP_OKAY))
+				dev_dbg_ratelimited(&info->xbdev->dev,
+					"Bad return from blkdev data request: %#x\n",
+					bret.status);
+
+			break;
+		default:
+			BUG();
+		}
+
+		if (likely(!blk_should_fake_timeout(req->q)))
+			blk_mq_complete_request(req);
+	}
+
+	rinfo->ring.rsp_cons = i;
+
+	if (i != rinfo->ring.req_prod_pvt) {
+		int more_to_do;
+		RING_FINAL_CHECK_FOR_RESPONSES(&rinfo->ring, more_to_do);
+		if (more_to_do)
+			goto again;
+	} else
+		rinfo->ring.sring->rsp_event = i + 1;
+
+	kick_pending_request_queues_locked(rinfo);
+
+	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+
+	xen_irq_lateeoi(irq, eoiflag);
+
+	return IRQ_HANDLED;
+
+ err:
+	info->connected = BLKIF_STATE_ERROR;
+
+	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+
+	/* No EOI in order to avoid further interrupts. */
+
+	pr_alert("%s disabled for further use\n", info->gd->disk_name);
+	return IRQ_HANDLED;
+}
+
+
+static int setup_blkring(struct xenbus_device *dev,
+			 struct blkfront_ring_info *rinfo)
+{
+	struct blkif_sring *sring;
+	int err;
+	struct blkfront_info *info = rinfo->dev_info;
+	unsigned long ring_size = info->nr_ring_pages * XEN_PAGE_SIZE;
+
+	err = xenbus_setup_ring(dev, GFP_NOIO, (void **)&sring,
+				info->nr_ring_pages, rinfo->ring_ref);
+	if (err)
+		goto fail;
+
+	XEN_FRONT_RING_INIT(&rinfo->ring, sring, ring_size);
+
+	err = xenbus_alloc_evtchn(dev, &rinfo->evtchn);
+	if (err)
+		goto fail;
+
+	err = bind_evtchn_to_irqhandler_lateeoi(rinfo->evtchn, blkif_interrupt,
+						0, "blkif", rinfo);
+	if (err <= 0) {
+		xenbus_dev_fatal(dev, err,
+				 "bind_evtchn_to_irqhandler failed");
+		goto fail;
+	}
+	rinfo->irq = err;
+
+	return 0;
+fail:
+	blkif_free(info, 0);
+	return err;
+}
+
+/*
+ * Write out per-ring/queue nodes including ring-ref and event-channel, and each
+ * ring buffer may have multi pages depending on ->nr_ring_pages.
+ */
+static int write_per_ring_nodes(struct xenbus_transaction xbt,
+				struct blkfront_ring_info *rinfo, const char *dir)
+{
+	int err;
+	unsigned int i;
+	const char *message = NULL;
+	struct blkfront_info *info = rinfo->dev_info;
+
+	if (info->nr_ring_pages == 1) {
+		err = xenbus_printf(xbt, dir, "ring-ref", "%u", rinfo->ring_ref[0]);
+		if (err) {
+			message = "writing ring-ref";
+			goto abort_transaction;
+		}
+	} else {
+		for (i = 0; i < info->nr_ring_pages; i++) {
+			char ring_ref_name[RINGREF_NAME_LEN];
+
+			snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
+			err = xenbus_printf(xbt, dir, ring_ref_name,
+					    "%u", rinfo->ring_ref[i]);
+			if (err) {
+				message = "writing ring-ref";
+				goto abort_transaction;
+			}
+		}
+	}
+
+	err = xenbus_printf(xbt, dir, "event-channel", "%u", rinfo->evtchn);
+	if (err) {
+		message = "writing event-channel";
+		goto abort_transaction;
+	}
+
+	return 0;
+
+abort_transaction:
+	xenbus_transaction_end(xbt, 1);
+	if (message)
+		xenbus_dev_fatal(info->xbdev, err, "%s", message);
+
+	return err;
+}
+
+/* Enable the persistent grants feature. */
+static bool feature_persistent = true;
+module_param(feature_persistent, bool, 0644);
+MODULE_PARM_DESC(feature_persistent,
+		"Enables the persistent grants feature");
+
+/* Common code used when first setting up, and when resuming. */
+static int talk_to_blkback(struct xenbus_device *dev,
+			   struct blkfront_info *info)
+{
+	const char *message = NULL;
+	struct xenbus_transaction xbt;
+	int err;
+	unsigned int i, max_page_order;
+	unsigned int ring_page_order;
+	struct blkfront_ring_info *rinfo;
+
+	if (!info)
+		return -ENODEV;
+
+	/* Check if backend is trusted. */
+	info->bounce = !xen_blkif_trusted ||
+		       !xenbus_read_unsigned(dev->nodename, "trusted", 1);
+
+	max_page_order = xenbus_read_unsigned(info->xbdev->otherend,
+					      "max-ring-page-order", 0);
+	ring_page_order = min(xen_blkif_max_ring_order, max_page_order);
+	info->nr_ring_pages = 1 << ring_page_order;
+
+	err = negotiate_mq(info);
+	if (err)
+		goto destroy_blkring;
+
+	for_each_rinfo(info, rinfo, i) {
+		/* Create shared ring, alloc event channel. */
+		err = setup_blkring(dev, rinfo);
+		if (err)
+			goto destroy_blkring;
+	}
+
+again:
+	err = xenbus_transaction_start(&xbt);
+	if (err) {
+		xenbus_dev_fatal(dev, err, "starting transaction");
+		goto destroy_blkring;
+	}
+
+	if (info->nr_ring_pages > 1) {
+		err = xenbus_printf(xbt, dev->nodename, "ring-page-order", "%u",
+				    ring_page_order);
+		if (err) {
+			message = "writing ring-page-order";
+			goto abort_transaction;
+		}
+	}
+
+	/* We already got the number of queues/rings in _probe */
+	if (info->nr_rings == 1) {
+		err = write_per_ring_nodes(xbt, info->rinfo, dev->nodename);
+		if (err)
+			goto destroy_blkring;
+	} else {
+		char *path;
+		size_t pathsize;
+
+		err = xenbus_printf(xbt, dev->nodename, "multi-queue-num-queues", "%u",
+				    info->nr_rings);
+		if (err) {
+			message = "writing multi-queue-num-queues";
+			goto abort_transaction;
+		}
+
+		pathsize = strlen(dev->nodename) + QUEUE_NAME_LEN;
+		path = kmalloc(pathsize, GFP_KERNEL);
+		if (!path) {
+			err = -ENOMEM;
+			message = "ENOMEM while writing ring references";
+			goto abort_transaction;
+		}
+
+		for_each_rinfo(info, rinfo, i) {
+			memset(path, 0, pathsize);
+			snprintf(path, pathsize, "%s/queue-%u", dev->nodename, i);
+			err = write_per_ring_nodes(xbt, rinfo, path);
+			if (err) {
+				kfree(path);
+				goto destroy_blkring;
+			}
+		}
+		kfree(path);
+	}
+	err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
+			    XEN_IO_PROTO_ABI_NATIVE);
+	if (err) {
+		message = "writing protocol";
+		goto abort_transaction;
+	}
+	info->feature_persistent_parm = feature_persistent;
+	err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
+			info->feature_persistent_parm);
+	if (err)
+		dev_warn(&dev->dev,
+			 "writing persistent grants feature to xenbus");
+
+	err = xenbus_transaction_end(xbt, 0);
+	if (err) {
+		if (err == -EAGAIN)
+			goto again;
+		xenbus_dev_fatal(dev, err, "completing transaction");
+		goto destroy_blkring;
+	}
+
+	for_each_rinfo(info, rinfo, i) {
+		unsigned int j;
+
+		for (j = 0; j < BLK_RING_SIZE(info); j++)
+			rinfo->shadow[j].req.u.rw.id = j + 1;
+		rinfo->shadow[BLK_RING_SIZE(info)-1].req.u.rw.id = 0x0fffffff;
+	}
+	xenbus_switch_state(dev, XenbusStateInitialised);
+
+	return 0;
+
+ abort_transaction:
+	xenbus_transaction_end(xbt, 1);
+	if (message)
+		xenbus_dev_fatal(dev, err, "%s", message);
+ destroy_blkring:
+	blkif_free(info, 0);
+	return err;
+}
+
+static int negotiate_mq(struct blkfront_info *info)
+{
+	unsigned int backend_max_queues;
+	unsigned int i;
+	struct blkfront_ring_info *rinfo;
+
+	BUG_ON(info->nr_rings);
+
+	/* Check if backend supports multiple queues. */
+	backend_max_queues = xenbus_read_unsigned(info->xbdev->otherend,
+						  "multi-queue-max-queues", 1);
+	info->nr_rings = min(backend_max_queues, xen_blkif_max_queues);
+	/* We need at least one ring. */
+	if (!info->nr_rings)
+		info->nr_rings = 1;
+
+	info->rinfo_size = struct_size(info->rinfo, shadow,
+				       BLK_RING_SIZE(info));
+	info->rinfo = kvcalloc(info->nr_rings, info->rinfo_size, GFP_KERNEL);
+	if (!info->rinfo) {
+		xenbus_dev_fatal(info->xbdev, -ENOMEM, "allocating ring_info structure");
+		info->nr_rings = 0;
+		return -ENOMEM;
+	}
+
+	for_each_rinfo(info, rinfo, i) {
+		INIT_LIST_HEAD(&rinfo->indirect_pages);
+		INIT_LIST_HEAD(&rinfo->grants);
+		rinfo->dev_info = info;
+		INIT_WORK(&rinfo->work, blkif_restart_queue);
+		spin_lock_init(&rinfo->ring_lock);
+	}
+	return 0;
+}
+
+/*
+ * Entry point to this code when a new device is created.  Allocate the basic
+ * structures and the ring buffer for communication with the backend, and
+ * inform the backend of the appropriate details for those.  Switch to
+ * Initialised state.
+ */
+static int blkfront_probe(struct xenbus_device *dev,
+			  const struct xenbus_device_id *id)
+{
+	int err, vdevice;
+	struct blkfront_info *info;
+
+	/* FIXME: Use dynamic device id if this is not set. */
+	err = xenbus_scanf(XBT_NIL, dev->nodename,
+			   "virtual-device", "%i", &vdevice);
+	if (err != 1) {
+		/* go looking in the extended area instead */
+		err = xenbus_scanf(XBT_NIL, dev->nodename, "virtual-device-ext",
+				   "%i", &vdevice);
+		if (err != 1) {
+			xenbus_dev_fatal(dev, err, "reading virtual-device");
+			return err;
+		}
+	}
+
+	if (xen_hvm_domain()) {
+		char *type;
+		int len;
+		/* no unplug has been done: do not hook devices != xen vbds */
+		if (xen_has_pv_and_legacy_disk_devices()) {
+			int major;
+
+			if (!VDEV_IS_EXTENDED(vdevice))
+				major = BLKIF_MAJOR(vdevice);
+			else
+				major = XENVBD_MAJOR;
+
+			if (major != XENVBD_MAJOR) {
+				printk(KERN_INFO
+						"%s: HVM does not support vbd %d as xen block device\n",
+						__func__, vdevice);
+				return -ENODEV;
+			}
+		}
+		/* do not create a PV cdrom device if we are an HVM guest */
+		type = xenbus_read(XBT_NIL, dev->nodename, "device-type", &len);
+		if (IS_ERR(type))
+			return -ENODEV;
+		if (strncmp(type, "cdrom", 5) == 0) {
+			kfree(type);
+			return -ENODEV;
+		}
+		kfree(type);
+	}
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
+	if (!info) {
+		xenbus_dev_fatal(dev, -ENOMEM, "allocating info structure");
+		return -ENOMEM;
+	}
+
+	info->xbdev = dev;
+
+	mutex_init(&info->mutex);
+	info->vdevice = vdevice;
+	info->connected = BLKIF_STATE_DISCONNECTED;
+
+	/* Front end dir is a number, which is used as the id. */
+	info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
+	dev_set_drvdata(&dev->dev, info);
+
+	mutex_lock(&blkfront_mutex);
+	list_add(&info->info_list, &info_list);
+	mutex_unlock(&blkfront_mutex);
+
+	return 0;
+}
+
+static int blkif_recover(struct blkfront_info *info)
+{
+	unsigned int r_index;
+	struct request *req, *n;
+	int rc;
+	struct bio *bio;
+	unsigned int segs;
+	struct blkfront_ring_info *rinfo;
+
+	blkfront_gather_backend_features(info);
+	/* Reset limits changed by blk_mq_update_nr_hw_queues(). */
+	blkif_set_queue_limits(info);
+	segs = info->max_indirect_segments ? : BLKIF_MAX_SEGMENTS_PER_REQUEST;
+	blk_queue_max_segments(info->rq, segs / GRANTS_PER_PSEG);
+
+	for_each_rinfo(info, rinfo, r_index) {
+		rc = blkfront_setup_indirect(rinfo);
+		if (rc)
+			return rc;
+	}
+	xenbus_switch_state(info->xbdev, XenbusStateConnected);
+
+	/* Now safe for us to use the shared ring */
+	info->connected = BLKIF_STATE_CONNECTED;
+
+	for_each_rinfo(info, rinfo, r_index) {
+		/* Kick any other new requests queued since we resumed */
+		kick_pending_request_queues(rinfo);
+	}
+
+	list_for_each_entry_safe(req, n, &info->requests, queuelist) {
+		/* Requeue pending requests (flush or discard) */
+		list_del_init(&req->queuelist);
+		BUG_ON(req->nr_phys_segments > segs);
+		blk_mq_requeue_request(req, false);
+	}
+	blk_mq_start_stopped_hw_queues(info->rq, true);
+	blk_mq_kick_requeue_list(info->rq);
+
+	while ((bio = bio_list_pop(&info->bio_list)) != NULL) {
+		/* Traverse the list of pending bios and re-queue them */
+		submit_bio(bio);
+	}
+
+	return 0;
+}
+
+/*
+ * We are reconnecting to the backend, due to a suspend/resume, or a backend
+ * driver restart.  We tear down our blkif structure and recreate it, but
+ * leave the device-layer structures intact so that this is transparent to the
+ * rest of the kernel.
+ */
+static int blkfront_resume(struct xenbus_device *dev)
+{
+	struct blkfront_info *info = dev_get_drvdata(&dev->dev);
+	int err = 0;
+	unsigned int i, j;
+	struct blkfront_ring_info *rinfo;
+
+	dev_dbg(&dev->dev, "blkfront_resume: %s\n", dev->nodename);
+
+	bio_list_init(&info->bio_list);
+	INIT_LIST_HEAD(&info->requests);
+	for_each_rinfo(info, rinfo, i) {
+		struct bio_list merge_bio;
+		struct blk_shadow *shadow = rinfo->shadow;
+
+		for (j = 0; j < BLK_RING_SIZE(info); j++) {
+			/* Not in use? */
+			if (!shadow[j].request)
+				continue;
+
+			/*
+			 * Get the bios in the request so we can re-queue them.
+			 */
+			if (req_op(shadow[j].request) == REQ_OP_FLUSH ||
+			    req_op(shadow[j].request) == REQ_OP_DISCARD ||
+			    req_op(shadow[j].request) == REQ_OP_SECURE_ERASE ||
+			    shadow[j].request->cmd_flags & REQ_FUA) {
+				/*
+				 * Flush operations don't contain bios, so
+				 * we need to requeue the whole request
+				 *
+				 * XXX: but this doesn't make any sense for a
+				 * write with the FUA flag set..
+				 */
+				list_add(&shadow[j].request->queuelist, &info->requests);
+				continue;
+			}
+			merge_bio.head = shadow[j].request->bio;
+			merge_bio.tail = shadow[j].request->biotail;
+			bio_list_merge(&info->bio_list, &merge_bio);
+			shadow[j].request->bio = NULL;
+			blk_mq_end_request(shadow[j].request, BLK_STS_OK);
+		}
+	}
+
+	blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);
+
+	err = talk_to_blkback(dev, info);
+	if (!err)
+		blk_mq_update_nr_hw_queues(&info->tag_set, info->nr_rings);
+
+	/*
+	 * We have to wait for the backend to switch to
+	 * connected state, since we want to read which
+	 * features it supports.
+	 */
+
+	return err;
+}
+
+static void blkfront_closing(struct blkfront_info *info)
+{
+	struct xenbus_device *xbdev = info->xbdev;
+	struct blkfront_ring_info *rinfo;
+	unsigned int i;
+
+	if (xbdev->state == XenbusStateClosing)
+		return;
+
+	/* No more blkif_request(). */
+	if (info->rq && info->gd) {
+		blk_mq_stop_hw_queues(info->rq);
+		blk_mark_disk_dead(info->gd);
+	}
+
+	for_each_rinfo(info, rinfo, i) {
+		/* No more gnttab callback work. */
+		gnttab_cancel_free_callback(&rinfo->callback);
+
+		/* Flush gnttab callback work. Must be done with no locks held. */
+		flush_work(&rinfo->work);
+	}
+
+	xenbus_frontend_closed(xbdev);
+}
+
+static void blkfront_setup_discard(struct blkfront_info *info)
+{
+	info->feature_discard = 1;
+	info->discard_granularity = xenbus_read_unsigned(info->xbdev->otherend,
+							 "discard-granularity",
+							 0);
+	info->discard_alignment = xenbus_read_unsigned(info->xbdev->otherend,
+						       "discard-alignment", 0);
+	info->feature_secdiscard =
+		!!xenbus_read_unsigned(info->xbdev->otherend, "discard-secure",
+				       0);
+}
+
+static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo)
+{
+	unsigned int psegs, grants, memflags;
+	int err, i;
+	struct blkfront_info *info = rinfo->dev_info;
+
+	memflags = memalloc_noio_save();
+
+	if (info->max_indirect_segments == 0) {
+		if (!HAS_EXTRA_REQ)
+			grants = BLKIF_MAX_SEGMENTS_PER_REQUEST;
+		else {
+			/*
+			 * When an extra req is required, the maximum
+			 * grants supported is related to the size of the
+			 * Linux block segment.
+			 */
+			grants = GRANTS_PER_PSEG;
+		}
+	}
+	else
+		grants = info->max_indirect_segments;
+	psegs = DIV_ROUND_UP(grants, GRANTS_PER_PSEG);
+
+	err = fill_grant_buffer(rinfo,
+				(grants + INDIRECT_GREFS(grants)) * BLK_RING_SIZE(info));
+	if (err)
+		goto out_of_memory;
+
+	if (!info->bounce && info->max_indirect_segments) {
+		/*
+		 * We are using indirect descriptors but don't have a bounce
+		 * buffer, we need to allocate a set of pages that can be
+		 * used for mapping indirect grefs
+		 */
+		int num = INDIRECT_GREFS(grants) * BLK_RING_SIZE(info);
+
+		BUG_ON(!list_empty(&rinfo->indirect_pages));
+		for (i = 0; i < num; i++) {
+			struct page *indirect_page = alloc_page(GFP_KERNEL |
+								__GFP_ZERO);
+			if (!indirect_page)
+				goto out_of_memory;
+			list_add(&indirect_page->lru, &rinfo->indirect_pages);
+		}
+	}
+
+	for (i = 0; i < BLK_RING_SIZE(info); i++) {
+		rinfo->shadow[i].grants_used =
+			kvcalloc(grants,
+				 sizeof(rinfo->shadow[i].grants_used[0]),
+				 GFP_KERNEL);
+		rinfo->shadow[i].sg = kvcalloc(psegs,
+					       sizeof(rinfo->shadow[i].sg[0]),
+					       GFP_KERNEL);
+		if (info->max_indirect_segments)
+			rinfo->shadow[i].indirect_grants =
+				kvcalloc(INDIRECT_GREFS(grants),
+					 sizeof(rinfo->shadow[i].indirect_grants[0]),
+					 GFP_KERNEL);
+		if ((rinfo->shadow[i].grants_used == NULL) ||
+			(rinfo->shadow[i].sg == NULL) ||
+		     (info->max_indirect_segments &&
+		     (rinfo->shadow[i].indirect_grants == NULL)))
+			goto out_of_memory;
+		sg_init_table(rinfo->shadow[i].sg, psegs);
+	}
+
+	memalloc_noio_restore(memflags);
+
+	return 0;
+
+out_of_memory:
+	for (i = 0; i < BLK_RING_SIZE(info); i++) {
+		kvfree(rinfo->shadow[i].grants_used);
+		rinfo->shadow[i].grants_used = NULL;
+		kvfree(rinfo->shadow[i].sg);
+		rinfo->shadow[i].sg = NULL;
+		kvfree(rinfo->shadow[i].indirect_grants);
+		rinfo->shadow[i].indirect_grants = NULL;
+	}
+	if (!list_empty(&rinfo->indirect_pages)) {
+		struct page *indirect_page, *n;
+		list_for_each_entry_safe(indirect_page, n, &rinfo->indirect_pages, lru) {
+			list_del(&indirect_page->lru);
+			__free_page(indirect_page);
+		}
+	}
+
+	memalloc_noio_restore(memflags);
+
+	return -ENOMEM;
+}
+
+/*
+ * Gather all backend feature-*
+ */
+static void blkfront_gather_backend_features(struct blkfront_info *info)
+{
+	unsigned int indirect_segments;
+
+	info->feature_flush = 0;
+	info->feature_fua = 0;
+
+	/*
+	 * If there's no "feature-barrier" defined, then it means
+	 * we're dealing with a very old backend which writes
+	 * synchronously; nothing to do.
+	 *
+	 * If there are barriers, then we use flush.
+	 */
+	if (xenbus_read_unsigned(info->xbdev->otherend, "feature-barrier", 0)) {
+		info->feature_flush = 1;
+		info->feature_fua = 1;
+	}
+
+	/*
+	 * And if there is "feature-flush-cache" use that above
+	 * barriers.
+	 */
+	if (xenbus_read_unsigned(info->xbdev->otherend, "feature-flush-cache",
+				 0)) {
+		info->feature_flush = 1;
+		info->feature_fua = 0;
+	}
+
+	if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0))
+		blkfront_setup_discard(info);
+
+	if (info->feature_persistent_parm)
+		info->feature_persistent =
+			!!xenbus_read_unsigned(info->xbdev->otherend,
+					       "feature-persistent", 0);
+	if (info->feature_persistent)
+		info->bounce = true;
+
+	indirect_segments = xenbus_read_unsigned(info->xbdev->otherend,
+					"feature-max-indirect-segments", 0);
+	if (indirect_segments > xen_blkif_max_segments)
+		indirect_segments = xen_blkif_max_segments;
+	if (indirect_segments <= BLKIF_MAX_SEGMENTS_PER_REQUEST)
+		indirect_segments = 0;
+	info->max_indirect_segments = indirect_segments;
+
+	if (info->feature_persistent) {
+		mutex_lock(&blkfront_mutex);
+		schedule_delayed_work(&blkfront_work, HZ * 10);
+		mutex_unlock(&blkfront_mutex);
+	}
+}
+
+/*
+ * Invoked when the backend is finally 'ready' (and has told produced
+ * the details about the physical device - #sectors, size, etc).
+ */
+static void blkfront_connect(struct blkfront_info *info)
+{
+	unsigned long long sectors;
+	unsigned long sector_size;
+	unsigned int physical_sector_size;
+	int err, i;
+	struct blkfront_ring_info *rinfo;
+
+	switch (info->connected) {
+	case BLKIF_STATE_CONNECTED:
+		/*
+		 * Potentially, the back-end may be signalling
+		 * a capacity change; update the capacity.
+		 */
+		err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+				   "sectors", "%Lu", &sectors);
+		if (XENBUS_EXIST_ERR(err))
+			return;
+		printk(KERN_INFO "Setting capacity to %Lu\n",
+		       sectors);
+		set_capacity_and_notify(info->gd, sectors);
+
+		return;
+	case BLKIF_STATE_SUSPENDED:
+		/*
+		 * If we are recovering from suspension, we need to wait
+		 * for the backend to announce it's features before
+		 * reconnecting, at least we need to know if the backend
+		 * supports indirect descriptors, and how many.
+		 */
+		blkif_recover(info);
+		return;
+
+	default:
+		break;
+	}
+
+	dev_dbg(&info->xbdev->dev, "%s:%s.\n",
+		__func__, info->xbdev->otherend);
+
+	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+			    "sectors", "%llu", &sectors,
+			    "info", "%u", &info->vdisk_info,
+			    "sector-size", "%lu", &sector_size,
+			    NULL);
+	if (err) {
+		xenbus_dev_fatal(info->xbdev, err,
+				 "reading backend fields at %s",
+				 info->xbdev->otherend);
+		return;
+	}
+
+	/*
+	 * physical-sector-size is a newer field, so old backends may not
+	 * provide this. Assume physical sector size to be the same as
+	 * sector_size in that case.
+	 */
+	physical_sector_size = xenbus_read_unsigned(info->xbdev->otherend,
+						    "physical-sector-size",
+						    sector_size);
+	blkfront_gather_backend_features(info);
+	for_each_rinfo(info, rinfo, i) {
+		err = blkfront_setup_indirect(rinfo);
+		if (err) {
+			xenbus_dev_fatal(info->xbdev, err, "setup_indirect at %s",
+					 info->xbdev->otherend);
+			blkif_free(info, 0);
+			break;
+		}
+	}
+
+	err = xlvbd_alloc_gendisk(sectors, info, sector_size,
+				  physical_sector_size);
+	if (err) {
+		xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
+				 info->xbdev->otherend);
+		goto fail;
+	}
+
+	xenbus_switch_state(info->xbdev, XenbusStateConnected);
+
+	/* Kick pending requests. */
+	info->connected = BLKIF_STATE_CONNECTED;
+	for_each_rinfo(info, rinfo, i)
+		kick_pending_request_queues(rinfo);
+
+	err = device_add_disk(&info->xbdev->dev, info->gd, NULL);
+	if (err) {
+		put_disk(info->gd);
+		blk_mq_free_tag_set(&info->tag_set);
+		info->rq = NULL;
+		goto fail;
+	}
+
+	info->is_ready = 1;
+	return;
+
+fail:
+	blkif_free(info, 0);
+	return;
+}
+
+/*
+ * Callback received when the backend's state changes.
+ */
+static void blkback_changed(struct xenbus_device *dev,
+			    enum xenbus_state backend_state)
+{
+	struct blkfront_info *info = dev_get_drvdata(&dev->dev);
+
+	dev_dbg(&dev->dev, "blkfront:blkback_changed to state %d.\n", backend_state);
+
+	switch (backend_state) {
+	case XenbusStateInitWait:
+		if (dev->state != XenbusStateInitialising)
+			break;
+		if (talk_to_blkback(dev, info))
+			break;
+		break;
+	case XenbusStateInitialising:
+	case XenbusStateInitialised:
+	case XenbusStateReconfiguring:
+	case XenbusStateReconfigured:
+	case XenbusStateUnknown:
+		break;
+
+	case XenbusStateConnected:
+		/*
+		 * talk_to_blkback sets state to XenbusStateInitialised
+		 * and blkfront_connect sets it to XenbusStateConnected
+		 * (if connection went OK).
+		 *
+		 * If the backend (or toolstack) decides to poke at backend
+		 * state (and re-trigger the watch by setting the state repeatedly
+		 * to XenbusStateConnected (4)) we need to deal with this.
+		 * This is allowed as this is used to communicate to the guest
+		 * that the size of disk has changed!
+		 */
+		if ((dev->state != XenbusStateInitialised) &&
+		    (dev->state != XenbusStateConnected)) {
+			if (talk_to_blkback(dev, info))
+				break;
+		}
+
+		blkfront_connect(info);
+		break;
+
+	case XenbusStateClosed:
+		if (dev->state == XenbusStateClosed)
+			break;
+		fallthrough;
+	case XenbusStateClosing:
+		blkfront_closing(info);
+		break;
+	}
+}
+
+static void blkfront_remove(struct xenbus_device *xbdev)
+{
+	struct blkfront_info *info = dev_get_drvdata(&xbdev->dev);
+
+	dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);
+
+	if (info->gd)
+		del_gendisk(info->gd);
+
+	mutex_lock(&blkfront_mutex);
+	list_del(&info->info_list);
+	mutex_unlock(&blkfront_mutex);
+
+	blkif_free(info, 0);
+	if (info->gd) {
+		xlbd_release_minors(info->gd->first_minor, info->gd->minors);
+		put_disk(info->gd);
+		blk_mq_free_tag_set(&info->tag_set);
+	}
+
+	kfree(info);
+}
+
+static int blkfront_is_ready(struct xenbus_device *dev)
+{
+	struct blkfront_info *info = dev_get_drvdata(&dev->dev);
+
+	return info->is_ready && info->xbdev;
+}
+
+static const struct block_device_operations xlvbd_block_fops =
+{
+	.owner = THIS_MODULE,
+	.getgeo = blkif_getgeo,
+	.ioctl = blkif_ioctl,
+	.compat_ioctl = blkdev_compat_ptr_ioctl,
+};
+
+
+static const struct xenbus_device_id blkfront_ids[] = {
+	{ "vbd" },
+	{ "" }
+};
+
+static struct xenbus_driver blkfront_driver = {
+	.ids  = blkfront_ids,
+	.probe = blkfront_probe,
+	.remove = blkfront_remove,
+	.resume = blkfront_resume,
+	.otherend_changed = blkback_changed,
+	.is_ready = blkfront_is_ready,
+};
+
+static void purge_persistent_grants(struct blkfront_info *info)
+{
+	unsigned int i;
+	unsigned long flags;
+	struct blkfront_ring_info *rinfo;
+
+	for_each_rinfo(info, rinfo, i) {
+		struct grant *gnt_list_entry, *tmp;
+		LIST_HEAD(grants);
+
+		spin_lock_irqsave(&rinfo->ring_lock, flags);
+
+		if (rinfo->persistent_gnts_c == 0) {
+			spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+			continue;
+		}
+
+		list_for_each_entry_safe(gnt_list_entry, tmp, &rinfo->grants,
+					 node) {
+			if (gnt_list_entry->gref == INVALID_GRANT_REF ||
+			    !gnttab_try_end_foreign_access(gnt_list_entry->gref))
+				continue;
+
+			list_del(&gnt_list_entry->node);
+			rinfo->persistent_gnts_c--;
+			gnt_list_entry->gref = INVALID_GRANT_REF;
+			list_add_tail(&gnt_list_entry->node, &grants);
+		}
+
+		list_splice_tail(&grants, &rinfo->grants);
+
+		spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+	}
+}
+
+static void blkfront_delay_work(struct work_struct *work)
+{
+	struct blkfront_info *info;
+	bool need_schedule_work = false;
+
+	/*
+	 * Note that when using bounce buffers but not persistent grants
+	 * there's no need to run blkfront_delay_work because grants are
+	 * revoked in blkif_completion or else an error is reported and the
+	 * connection is closed.
+	 */
+
+	mutex_lock(&blkfront_mutex);
+
+	list_for_each_entry(info, &info_list, info_list) {
+		if (info->feature_persistent) {
+			need_schedule_work = true;
+			mutex_lock(&info->mutex);
+			purge_persistent_grants(info);
+			mutex_unlock(&info->mutex);
+		}
+	}
+
+	if (need_schedule_work)
+		schedule_delayed_work(&blkfront_work, HZ * 10);
+
+	mutex_unlock(&blkfront_mutex);
+}
+
+static int __init xlblk_init(void)
+{
+	int ret;
+	int nr_cpus = num_online_cpus();
+
+	if (!xen_domain())
+		return -ENODEV;
+
+	if (!xen_has_pv_disk_devices())
+		return -ENODEV;
+
+	if (register_blkdev(XENVBD_MAJOR, DEV_NAME)) {
+		pr_warn("xen_blk: can't get major %d with name %s\n",
+			XENVBD_MAJOR, DEV_NAME);
+		return -ENODEV;
+	}
+
+	if (xen_blkif_max_segments < BLKIF_MAX_SEGMENTS_PER_REQUEST)
+		xen_blkif_max_segments = BLKIF_MAX_SEGMENTS_PER_REQUEST;
+
+	if (xen_blkif_max_ring_order > XENBUS_MAX_RING_GRANT_ORDER) {
+		pr_info("Invalid max_ring_order (%d), will use default max: %d.\n",
+			xen_blkif_max_ring_order, XENBUS_MAX_RING_GRANT_ORDER);
+		xen_blkif_max_ring_order = XENBUS_MAX_RING_GRANT_ORDER;
+	}
+
+	if (xen_blkif_max_queues > nr_cpus) {
+		pr_info("Invalid max_queues (%d), will use default max: %d.\n",
+			xen_blkif_max_queues, nr_cpus);
+		xen_blkif_max_queues = nr_cpus;
+	}
+
+	INIT_DELAYED_WORK(&blkfront_work, blkfront_delay_work);
+
+	ret = xenbus_register_frontend(&blkfront_driver);
+	if (ret) {
+		unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
+		return ret;
+	}
+
+	return 0;
+}
+module_init(xlblk_init);
+
+
+static void __exit xlblk_exit(void)
+{
+	cancel_delayed_work_sync(&blkfront_work);
+
+	xenbus_unregister_driver(&blkfront_driver);
+	unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
+	kfree(minors);
+}
+module_exit(xlblk_exit);
+
+MODULE_DESCRIPTION("Xen virtual block device frontend");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_BLOCKDEV_MAJOR(XENVBD_MAJOR);
+MODULE_ALIAS("xen:vbd");
+MODULE_ALIAS("xenblk");